In the field of veterinary medicine, except at major centers, the principal treatment modality for solid malignancies in pet animals in surgery. Both for potential veterinary use and to advance our knowledge for future human clinical trials, we propose to assess the use of Photodynamic Therapy (PDT) in solid tumors in pet animals. Analyzed by size, histology, and anatomical location we will first determine survival rates at one year after treatment and patterns of failure following a set protocol and then determine both tumor and normal tissue response to PDT as drug (Photofrin II) dose and light dose are varied. Following the establishment of an optimal treatment regimen, additional studies will be conducted to determine if modifications in tissue optical dose distribution can enhance the overall efficacy of treatment.